Compensated meter



A. e. GRIER COMPENSATED METER Filed D60- 1925 5 ACCURACY 3:

- JHUNT HAvmo \NEGATIV TEMPERATURE CQEFFICIEHT 21 lEEMEABILITY Inventor Arthur G. Grier;

His Attorney- Patented July 10,

UNITED PATENT: i orrioa.

ARTHUR-d, cams, on rmnnaono, CANADA, assrenon To enn anannnnc'rmo.

- COIPANZZA conronarron or NEW YORK. v I

collrmrsarzan METER ap ueaueialea December a, was. Serial magma.

My invention relates to the overload coinpensation of electric meters and its purpose is to improve the accuracy of meters when subjected to overload conditions.

7 It isgenerally known that the active magnetic flux from the current coil or coils of the induction disc type watthour meter .produces a retarding torque on' the disc asv well as cooperating with the potential flux to ro- 1 duce a driving'torque on the disc. The riving torque increases as the first power of the current flux and predominates to such an extent over the retarding influence of Y this flux that up to about 125 per cent of the normal rating of the meter the retarding effect does not seriously interfere with .the accuracy of the meter. However, the retarding eilect of the current flux increases as the square of. the current so thatit becomes sufliciently large above 125 r cent normal load as to perceptibl slow own the 'meter. The examination, 0 the load char acteristic curve of the average induction disc watthour meter shows that the curve drops rapidly at 200 per cent load and above. Although the average induction meter will carry overloads of. 300 per cent with safety,-

it is usually not considered good practice to operate them for any length of time at loads much above 125per cent normal due to the loss in revenue resulting from the meter running slow above. this ppint. My invention relates to a method and means of compensating for overload errors of induction meters so that they can be operated at higher loads without the resulting loss in revenue. In carrying my invention nto efiect provide temperature responsive means influenced by overload conditions for reducing the meter damping during overloads to sue an extent as to 'make the meter speed substantially proportional to the load. 7

The f tures of'my invention which are believed to be novel and patentable will, be

ointed out in the claims ap ended hereto.

reference is made in the following description to the accompanying drawings, Fig. 1 of which represents a modification of my the damping magnet system of a meter, the shunt being moved to shunt more or less of the damping flux in res onse to a temperature responsive inember eated by the meter to the le ture responsive means heate ,spring with its free end. slidably engaging "the tem rature responsive spring 23 by means 0 a knife ed e joint at 25 formed by or a better understanding 0 my invention p,

invention employingflan adjustable shunt for' 24..

load current; Fig.1 illustrates the nature of l the connection between members 23 and 24, Fig. 1; Fig. 2 represents a modification where the damping flux is varied in response to changes in permeability of a portion of the damping magnetic system which has a negative tem rature coeflicient of permeability; and ig. 3 represents comparative load curves of an induction meter with an without over-load compensation.

Referring to Fig. 1 f the draw1ng,10'

represents the rotary disc secondary of an induction'watthour meter, 11 is a supportin 'plate of the meter from which the usua damping magnet system 12 for the disc 10 is supported. The current. and potential" coils of the meter are diagrammaticall represented at 13 and 14 res ctively an they are connected in the usua manner with the circuit 15 to be metered. 16 represents a magnetic shunt secured toan arm 17 which is pivoted at 18. The shunt is represented in the normal load position and this position may be adjusted by the adjustable stop 19. In the position represented the shunt 16 will have a negligible influenceon the damping magnet s stem but if it is moved graduall from theposition shown it wi l shunt more 2and more of thefflux of the permanent magnets between the upper 11 and s poles and less will pass through the disc 10, there y decreasing thedamiing. Tem raby the loa current 1s provided 'to rotate arm 17 to the left about its pivot 18 so as to decrease the effective dampin flux of the meter in pro- 90 portion to over oads. Forthis purpose I. provide a heating element 22 through which the load current or a proportional art thereof is conducted as by connecting t e heating element in series with the current coil of the meter as represented. Secured to and in good heat conducting relation with heating element 22 is a bimetallic sprin 23 and se-- cured to theuppefend of arm 1 is a second passin spring 23 t rou h a slitin sprin Vh'en a predetermined overload cur rent flows through the circuit including the heating element 22, spring 23 will be heated and deflected downward, thereby rotating spring 24 and arm 17 aboutpivot point 18,

, pose of -spring 24 is to compensate the deand moving shunt 16 to the left. 'The purvicefor ordinary room. temperaturechanges not caused by overload conditions. Thus if the deflection of spring 23 is caused by normal heating conditions spring 24 will .bede- 'flected downward to the same extent and there will be no movement of arm 17. 'But if spring 23 is deflected to a greater extent due to overload conditions the arm 17 will be moved. The overload at which arm 17 starts to move and its law of movement at higher overload-s may be adjusted by the zero sto 19, the initial positions of the springs an the heating influence of element 22. The ordinary induction watthour meter has an accuracy varying with load as represented by the full line curve A of Fig. 3. At'about 125 per cent load the meter starts to operate too slowly and becomes less accurate as the load increases. By my invention the damping of the meter at these overloads is decreased. in the manner described without interfering with the driving torque in any way so that the accuracy of the meter becomes substantially 100 percent as represented by the dotted line B of Fig. 3.

InFig. 21' have shown another arrangement for accomplishin the same result. In this figure reference c aracters 10, '14 and 15 have the same significance as in Fig. 1.

The current coil and its core being beneath the disc are not shown. The damping magnet system comprises the permanent magnet .26 above the disc and themagnetic bar 27 beneath the disc. In this. case the damping flux passes from one ole of the ermanent magnet 26 through t e disc to t e bar 27, then back through the disc to the other pole of the permanent magnet. The damping the manner described in application Serial No. 711,023, filed May 5, 1924, to Isaac F. Kinnard. This bar is arranged to be heated by a resistance 28 supplied from a current transformer 29 connected in the meter load circuit 15. Since this resistance is supplied from a current transformer 29 the currentflowing therein will be pro ortioinal to the load current irres ective 0 chan esv in the resistance value 0 29 which may e due to changes in temperature. Thus even though the resistance 29 be'made of a material having apositive temperature coeflicient of resistance its heating effect will increase with load current because the characteristics of ,secondary burden.

a current transformer are such as to maintam substantially a constant current transformer ratio irrespective of changes in the The thermal characteristics of member 27 are so proportioned as to decrease the permeability 'of member 27 as an overload comes on the meter, thereby decreasing the damping flux passing throu h the disc in an amount to compensate for t e .increasing damping'influenceof the current flux of the meter. I

In those rare cases where the volta e of the metered circuit fluctuates considera meter will increase to: such an extent as to produce an erroneous damping influence at excessive voltage. My invention is equally applicable to correct for such' conditions simply by making the heating of the -elements 22 and 28 in Figs. 1 and 2 respectively responsive to excessive voltages. The invention is not limited to induction type watthour meters but may be applied for example to induction reactive component meters.

In accordance with the provisions of the patent statutes I have described the principle of operation of my invention together with the apparatus which I now consider to represent the best embodimentthereof; but I desire to have it understood that'the apparatus shown and described is only illustrative and thatthe invention may be carried out by othermeans.

.VVhat I claim as new and desire to secure by Letters Patent of the United States is 1. An induction type watthour meter hav ing a tendency to run too slowly when subjected to an overload current, and means responsi've to such overload current for decreasing the damping of said meter to compensate for such tendency.

2. An integrating electric meter of the induction type having damping means for the rotary element of said meter, and means responsive only to overload conditions on said meter for decreasing the damping of said meter. 7

The method of compensating integrating type induction meters for the damping error produced by overload flux conditions of the driving elect-romagnet which consists in decreasing the damping of said meter in proportion to such conditions.

4. An induction type meter having damping means and thermal means responsive to the load current of said meter for decreasing the damping influence of said damping means when the load currentis above a predetermined value.

5. An integrating type induction meter having permanent magnet damping means, a driving electromagnet which produces a dam ing. flux \under overload conditions tending tomake the meter run too slow andmeans respbnsiv'e to the current producing ly it 1nay happen that the potential flux of the such 'flux for decreasing permanent mag- I .net meter damping in proportion to the damping effect of said flux. i g

6. An integrating type induction meter having the usual damping and driving magnet systems, the drivin fmagnet system having-a coil traversed .by t e load current which produces a damping flux under overload conditions tending to make the meter" run too slow, a heating element traversed by the load current, and thermal responsive means influenced-by said heating element for'va-rying the usual damping flux of said meter-1n a manner to compensate for the; tendency for said meter to run slow underovere load conditions.

' 7Q An integrating type induction meter having damping means,.a temperature responsive elementsmeans for heatmg said element in proportion to a load condition ofv said meter, a second temperature responsive element responsive to room temperatures only, and means controlled jointly by said two temperature responsive elements for varying the damping of said meter in response to the aforesaid load condition.

8. A meter, a temperature responsive element responsive to load conditions of said meter, a temperature responsive means re- 'sponsive to room temperature only, means controlled jointly by said two temperature responsive means for varying the operation of said meter, and means for rendering said temperature responsive means inactive to control the operation of'said meter under certain load conditions.

9. An integrating type induction. meter having damping means, a temperature responsive element responsive to the load currentof said meter, a temperature responsive means responsive to room temperature only, means controlled jointly by said temperature responsive means for decreasing the damping of said'meter'with increase in load cur-' -'sive means compensated for changes in room temperature for moving said shunt in response to predetermined overload conditions on said meter.

In witness whereof I have hereunto set my hand this thir'drday of December, 1925.

ARTHUR G. Gui-ER; 

